1. Field of the Invention
This invention relates to an objective lens supporting apparatus of an optical pickup for recording information on and reproducing information from a recording medium such as optical disks including a compact disk (CD), a digital versatile disk (DVD), a laser disk (LD), a magnetic optical disk (MO), and a mini disk (MD).
2. Description of the Related Art
An optical pickup for optically reading information recorded on a disk type medium such as a compact disk (CD) or a digital versatile disk (DVD), and for outputting the read information as an electric signal conventionally includes an objective lens supporting apparatus. The objective lens supporting apparatus is operated in such a way as to follow a motion of the disk.
The objective lens supporting apparatuses are roughly classified into a shaft slide type and a wire support type.
An objective lens supporting apparatus of the shaft slide type has an objective lens attached to a lens frame, and a drive coil attached to a side face of the lens frame. A sliding shaft extending in the direction of an optical axis of the objective lens is fixed to an optical pickup body. The sliding shaft penetrates the lens frame. The lens frame is rotatable about the sliding shaft. The lens frame is displaced around the sliding shaft in order to perform tracking servo control. Further, the lens frame is slid in the direction of the shaft in order to perform focusing servo control.
On the other hand, objective lens supporting apparatuses of the wire support type are disclosed in JP-A-6-223393, JP-A-8-7303, JP-A-9-306003 and JP-A-10-143886. The objective lens supporting apparatus includes a lens frame having an objective lens, a focusing coil and a tracking coil. The lens frame is supported by a wire-like elastic support element on an optical pickup body in a cantilevered manner. A magnetic circuit, which is used for generating magnetic fluxes acting on the focusing coil and the tracking coil and consists of a permanent magnet and a yoke, is provided on the optical pickup body. In this configuration, the objective lens is driven in a focusing direction and a tracking direction by selectively energizing the focusing coil and the tracking coil by the wire-like elastic member in order to perform focusing and positioning on the optical axis.
The rotational speed of a disk such as a CD or a DVD is increasing in accordance with an increase in the read speed or the write speed of a CD drive apparatus or a DVD drive apparatus. Therefore, a high focusing speed and high-speed tracking capability are required.
A lens having a high numerical aperture is often used for an optical disk such as a DVD, on which information is recorded with high density and which has extremely narrow track intervals. In case that the lens having a high numerical aperture is used, the influence of comatic aberrations generated owing to inclination of an optical disk, which is caused by the warpage of the disk itself and the axial runout occurring during the rotation thereof, becomes serious. Thus, there has been increasing need for maintaining the tilt angle of the objective lens and the relative angle of the optical disk in ideal conditions even when the objective lens moves from right to left or up and down in accordance with the rotation of the optical disk for focusing. Also, need for reading information more quickly and accurately is increasing.
However, the aforementioned objective lens supporting apparatus of the sliding shaft type has drawbacks in that the friction resistance is generated between the sliding shaft and the lens frame when the sliding shaft slides and the lens frame rotates therearound. Thus the focusing speed becomes relatively low and the tracking capability becomes poor, and it is difficult to increase the read speed and the write speed to high levels. Since the sliding shaft is passed through the lens frame, it is necessary to incline the sliding shaft in accordance with the inclination of the optical disk to enable the inclination of the objective lens to follow the minute inclination of the optical disk during reading or writing the information in such a way as to make the optical axis of the objective lens perpendicular to the surface of the optical disk. Consequently, the size and the weight of a movable body become large and it becomes difficult to perform high-speed tracking.
On the other hand, the objective lens supporting apparatus of the wire support type as described in the above has a simple structure and a movable body can be configured to be light. Thus, this objective lens supporting apparatus is excellent at the focusing speed and the high speed tracking capability. Consequently, an objective lens supporting apparatus of the wire support type having a drive apparatus for inclining the objective lens in such a way as to follow the inclination of the disk during rotation of the disk to thereby set the optical axis of the objective lens nearly perpendicular to a read face of the disk has been desired.